What Is MPGe?

MPGe is the abbreviation for “miles per gallon of gasoline-equivalent.” It’s an energy efficiency metric that was introduced by the Environmental Protection Agency (EPA) in 2010 to compare the amount of energy consumed by alternative fuel vehicles to that of traditional gas-powered cars. If a vehicle uses non-liquid fuels that aren’t burned and gets its power from electricity or compressed natural gas, it’s rated in MPGe. This is the calculation you will see on an electric car’s window sticker.

How Is MPGe Calculated?

According to the EPA, burning one gallon of gas produces 115,000 BTUs (British thermal units). To generate the same amount of heat by way of electricity, it takes 33.7 kilowatt-hours (kWh). Kilowatt-hours is the standard energy unit for electricity.

In simplified terms, if an electric vehicle can travel 100 miles on 33.7 kWh of electricity, the EPA rates it at 100 MPGe. As you can see, this would be a very efficient vehicle, because a gas car would have to travel 100 miles per gallon to be equivalent.

A Better Way to Determine Electric Car Costs

While a car’s MPGe number is a good way to compare its energy consumption to that of a gas-powered car, it’s not helpful in determining a vehicle’s fuel costs. If an electric car gets 136 MPGe compared to a gas car’s 32 MPG, it’s clear that the electric car is significantly more efficient, but how much does electricity cost at 136 MPGe? That question doesn’t really make sense, but the EPA provides another metric we can use to find the answer.

The EPA’s window sticker also specifies a car’s kilowatt-hours-per-100-miles rating (kWh/100 mi), or the number of kWh necessary to travel 100 miles. This rating gives you a solid idea of how good a vehicle is at turning its electricity into miles of range. Keep in mind that the numbers are flipped (kWh per mile instead of miles per kWh, which would be more similar to miles per gallon). Therefore, unlike miles per gallon (where a higher number is better), the lower the number of kilowatt hours required to go 100 miles, the better.

For context, the 2018 Hyundai Ioniq Electric is rated at 25 kWh/100 miles. It comes with a 28-kWh battery pack, which is capable of 124 total miles. The EPA says the annual electricity cost for the Ioniq Electric is only $500, with the assumption of 15,000 miles traveled and a projected electricity price.

In comparison, a base 2018 Tesla Model X 75D gets 36 kWh/100 miles and will cost you about $700 per year. Even though the Model X is one of the most inefficient EVs, it still offers substantial savings over paying for gas. The comparably sized and priced 2018 Porsche Cayenne will cost you $2,550 to fuel for a year. Even the more efficient 2018 Porsche Cayenne S-E Hybrid has well over double the fuel costs of the Model X, at $1,950 annually.

How Does It All Add Up?

Keep in mind that electricity rates vary geographically, just like gas prices. At the time of this writing, the average U.S. price for electricity was 12.89 cents per kWh. April 2018 rates show the lowest price in Washington, at 9.74 cents per kWh, and the highest price in Hawaii, at 31.21 cents. Hawaii is an outlier though, since the next most expensive state is Massachusetts, at 22.34 cents.

Hyundai Ioniq Electric (Hyundai Motor America)

Let’s do some quick math here. If you live in Washington, you can travel 100 miles in a Tesla Model X 75D (the least efficient electric car on our list) for $3.51. If you opt for the most efficient electric vehicle on the market today, the Hyundai Ioniq Electric, you’re looking at a 100-mile cost of a mere $2.44. If you happen to live in Massachusetts, the Model X will cost you $8.04 for 100 miles, and the Ioniq sits at $5.59.

Even if you live in Hawaii, where prices for electricity are exorbitant, your electric-car fuel savings are significant. At the lowest gas prices in the island state (around $3.64), even the most fuel-efficient hybrid cars cost more to fuel than EVs.

Since we think about gas based on the price per gallon, we’ll look at one more telling, side-by-side comparison. The 2018 Ford Focus and Ford Focus Electric are essentially the same car, aside from powertrain. The base gas-powered Focus returns 31 mpg combined, and the Focus Electric uses 31 kWh/100 miles. At the time of this writing, the average U.S. price for gas was $2.86, meaning that’s what it should cost you to travel those 31 miles in the Focus. Using the average 12.89 cents per kWh, the Focus Electric will travel the same 31 miles for $1.24.

Battery Electric Vehicles With the Best MPGe

The following table shows current 2018 battery-electric vehicles with the best EPA-estimated MPGe, as well as average kilowatt-hours used per 100 miles traveled. The EPA also provides an estimated annual electricity cost and total range for each vehicle.

Keep in mind that these are base models. Typically, upper trims provide better performance and will have a lower MPGe rating. For example, BMW added an i3s (Sport) model for 2018. It returns a combined 6 MPGe less than the base model and has 7 fewer miles of range. Tesla offers multiple trims beyond its 75D models, and each higher trim is progressively less efficient. However, due to Tesla’s higher trims having a larger battery pack, range increases.